The present invention relates to xe2x80x9cactive implantable medical devicesxe2x80x9d as such devices are defined by the Jun. 20, 1990 directive 90/385/CEE of the Council of the European Communities, more particularly to pacemaker, defibrillator and/or cardiovertor devices which are able to deliver to the heart low energy stimulation pulses for the treatment of the cardiac rate disorders, and even more particularly to the so-called xe2x80x9cmultisitexe2x80x9d prostheses in which electrodes are placed in a plurality of distinct respective cardiac sites, comprising at least one ventricular site and one atrial site.
Multisite prosthesis are known and include the following types: xe2x80x9cdouble chamberxe2x80x9d (right atrial stimulation and right ventricular stimulation), xe2x80x9ctriple chamberxe2x80x9d (right atrial stimulation and double ventricular stimulation), and xe2x80x9cquadruple chamberxe2x80x9d (double atrial stimulation and double ventricular stimulation).
In addition to the treatment of cardiac disorders, it has been proposed to treat by stimulation myocardial contraction disorders which are observed among patients having a cardiac insufficiency. These disorders may be spontaneous or induced by a traditional stimulation pulse. One will be able, in particular, to refer to the study of J. C. Daubert et al., Stimucoeur, 25, nxc2x03, pp. 170-176, which gives a report on work with respect to this subject.
Daubert et al. proposed to stimulate simultaneously and permanently the left and right ventricles, for the resynchronization of both ventricles. One often can observe spectacular results by such treatment for patients having a Class-III type cardiac insufficiency, whose condition was not improved by the traditional treatments.
In practice, multisite devices preferably operate in synchronous stimulation. This means that the two ventricular stimulation sites receive stimulation pulses at the same time, i.e., there is no inter-ventricular delay. This is also called a bi-ventricular stimulation.
The starting point of the present invention lies in the observation by the inventors that this bi-ventricular stimulation with no inter-ventricular delay is not necessarily optimal, and, further, does not necessarily lead to a synchronous contraction of the two ventricles. Indeed, the times of conduction within the myocardium are not the same on the right and on the left sides, and the variance can depend on multiple factors, such as the site of the left ventricular probe, according to whether this probe is placed in the coronary sinus or an epicardial probe.
It is therefore, an object of the present invention to propose a device that is able to establish an inter-ventricular delay between two ventricular stimulations, and to adjust this delay so as to resynchronize the contraction of the ventricles, and thus to lead to a fine optimization of the patient""s hxc3xa9modynamic condition.
Broadly, the present invention is directed to a device which is, in a way in itself known, a device of the multisite type, for use with electrodes that are placed in at least two cardiac sites, right and left. These electrodes are connected to a circuit in the device for the collection (i.e., the sensing or detection) of cardiac signals, more specifically to detect a depolarization potential, as well as to a circuit in the device for the stimulation of the heart, more specifically to apply stimulation pulses to at least certain of the aforesaid sites.
According to the invention, the device also comprises means for resynchronization of the ventricular contractions, with means for establishing an inter-ventricular delay between the time of application of the respective stimulation pulses on the right and left ventricles, means for determining a parameter representative of the degree of synchronization between the ventricles and analyzing this parameter, and means for varying the inter-ventricular delay in the direction of the improvement of the aforesaid representative parameter.
According to an advantageous subsidiary characteristic of the invention, the means for determining the representative parameter comprise a hemodynamic sensor, in particular a sensor of an intracardiac bio-impedance measured dynamically between a right site and a left site, more preferably between a right ventricular site and a left ventricular site, or between a right atrial site and a left ventricular site. The measurement of impedance is preferably operated by injection of a current pulse between the right and left sites, and the collection of a differential potential between a right site and a left site, or between two right sites, or between two left sites.
The configuration of the bio-impedance measurement can be a quadripolar configuration, without a site common to the injection and the collection, or a tripolar configuration, with one site common to the injection and the collection. One particular a configuration is where the site common to the injection and the collection is a left ventricular distal site, the other injection site is a distal right ventricular site, and the other collection site is a right ventricular proximal site.